I discovered and installed nethserver last week and have become more and more enthusiastic because of the simplicity of installing and configuring everything and how complete nethserver is. I have the applications NextCloud, Samba and Webtop installed with a Let Encrypt certificate and everything works well except for one thing and that is Active Sync. I have read the manuals, searched nethserver.org and the Internet but cannot find an answer to solve the problem.

Could this be SELinux related (this deals with CentOS defaults shipping it with httpd not being able to create outbound connections, as is required for modproxy to work, and would probably not be relevant for a clean install from a NethServer iso) Test is simple:

I do have a question, what is the reason why the /var/log/httpd/ssl_error_log is filled with this error messages? Could there be perhaps a problem with the certificate? From outside the certificate works well but could there be perhaps an other problem for the internal requests?

All I can find is port 20000 will be used but there is no listener on port 20000.

which program or service is missing that should listen to port 20000 ???

SOGo listens on port 2000. This is why you need to check your httpd configuration: you need to switch from SOGo to WebTop fro Active Sync configuration. The commands I gave you before should do the job unless something is wrong in your machine.